Owing to excellent display performances and low power consumption, thin film liquid crystal displays have come to prevail as display devices for portable personal computers and television. Any liquid crystal display has a sandwich structure in which a liquid crystal display device is interposed between transparent electrically conductive films.
Transparent electrically conductive films for use in these display devices are generally formed by a sputtering method using a sintered body target. As a material for the target, conventionally, an indium-tin oxide (to be abbreviated as “ITO” hereinafter) has been used. That is because a transparent electrically conductive film formed from the ITO target has high light transmittance and further has excellent electrical conductivity. However, the transparent electrically conductive film formed from the ITO target has a problem that since the etching thereof requires a strong acid such as aqua regia, hydrochloric acid or hydrobromic acid, a wiring material in a thin film liquid crystal display may be ultimately also etched.
For overcoming the above problem, therefore, JP-A-6-234565 and JP-A-6-318406 propose a method in which a film is formed from a sputtering target formed of a zinc-oxide-indium-oxide-containing material. When a transparent electrically conductive film formed from the above sputtering target formed of a zinc-oxide-indium-oxide-containing material is used, a weak acid such as oxalic acid can be used, so that the wiring material in a thin film liquid crystal display is no longer likely to be ultimately etched. Since, however, the above sputtering target formed of a zinc-oxide-indium-oxide-containing material has a high volume resistivity itself, there is caused a problem that the target breaks or causes abnormal discharge during sputtering.
Further, for decreasing the volume resistivity of the above sputtering target formed of a zinc-oxide-indium-oxide-containing material, JP-A-9-71860 proposes a sputtering target formed by adding an oxide of a metal having a normal valence of 3 or more to a zinc-oxide-indium-oxide-containing material. However, there is a problem that a transparent electrically conductive film formed from the above target has no sufficient etching property, although the volume resistivity of the target can be decreased by adding an oxide of a metal having a normal valence of 3 or more.
It is an object of the present invention to provide a sputtering target that has a low volume resistivity and permits stable sputtering, and a transparent electrically conductive film that is formed from the target and is excellent in etchability.
The present inventors have made diligent studies, and as a result, it has been found that the above object can be achieved by a sputtering target containing a hexagonal laminar compound formed of indium oxide and zinc oxide and further containing an oxide of a third element having a normal valence of 4 or more. On the basis of the above finding, the present invention has been completed.